This invention relates to systems and methods for controlling process equipment temperatures, and more particularly to operator and automatically controllable digital systems for versatile modular based temperature control units.
Digital control systems for process equipment and tools that are used for complex manufacturing procedures are known and in use in a wide variety of practical applications. Often, such systems are used to maintain one or a number of operating parameters at chosen static or variable setpoints during an operation or process. Control algorithms are used to interrelate sensed variables to target conditions, and to bring a controlled parameter to a chosen setpoint.
An important example of this use of control systems is in the operation of temperature control units (TCU) which heat or cool, in selectable fashion, one or more particular subunits of cluster tools employed in semiconductor fabrication. For some semiconductor fabrication process tools, TCU""s may have to refrigerate or heat at different levels, changing levels when needed for the process. Usually, the temperature control is accomplished by circulating a thermal transfer fluid through the tool at temperatures and flow rates suitable for each given operating setpoint. Because cluster tool capital equipment and operating costs are very high, the temperature control units and their associated digital control systems must operate with maximum reliability and minimum down time. Moreover, steady state operation at a given temperature level is often required to be very precise while transition or ramp times between different steady state levels are desirably as short as possible.
Operation of such systems in practice, however, entails much more than operating stability and minimization of transition intervals. Initial installation, system setup, system monitoring and adjustment, trouble-shooting and field service are all factors which affect the economics and eases of use. In addition, TCU types and capabilities can vary substantially for a given cluster tool installation. For example, a new multi-TCU system has been introduced which is based on a modular approach in which different but interchangeable TCU modules are used. The modules each have at least two and up to four functional capabilities including both heating and cooling, and can have substantially different thermal capacities. Such TCU modules can control different subunits in a cluster tool, while meeting operational needs economically and in a space efficient manner. This approach also minimizes field service problems because troublesome and defective modules may quickly be replaced and either serviced on site or shipped to a common service facility. Generally, the different modular TCU""s each have both heating and cooling capability, which can be exercised at the same time or independently.
A control system and method for operating different modules concurrently in different modes must present the options in such a way that the operator can be guided through the setup sequence and make needed choices without extensive pre-education or specialization. After setup, the operation should also be assisted with information at to real time operating conditions, significant changes in conditions, warning of problems and guidance as to how they can be resolved. Changes in the modular setup should be accommodated, and the control system should also be responsive to remote commands from a host system.
The digital control systems used for process control applications, being the process variable to a chosen operating setpoint and thereafter maintain the target setpoint with a closed loop servo approach. For improved response the servo loop follows a control algorithm, such as the PID (proportional, integral and derivative terms) algorithm to bring a process variable to a target level. A typical modern system using an algorithm of this type is designated model S7-200 and is a product of the Siemens Company. This digital control system includes programmed logic circuits, memory and software, together with various sensed inputs, for exercising the PID control algorithm. It operates in scanning sequences and includes expansion modules so that more than one process variable can be controlled concurrently. This control systems is not, by itself, capable of meeting more demanding requirements, such as those imposed on TCU""s employed for control of semiconductor fabrication tool processes. For semiconductor fabrication processes, it is essential that steady state temperatures be very precisely maintained, but that transitions between different temperature levels be rapid. The heating and cooling capabilities must be used in making these changes, with maximum power efficiency. In addition, environmental and other variables which can arise must be compensated for. Because of the high capital and operating costs involved in semiconductor fabrication facilities, the system should also be capable of communicating information as to status and operating conditions, non-standard conditions, setup, warnings and alarms. Preferably, it should also automatically terminate operations when necessary.
A control and display system in accordance with the invention for a reconfigurable and complex control system having multiple control units accepts a variety of real time inputs and setpoints and generates commands for commanding individual units to regulate process variables. The commands are variable with time and based upon adaptive control algorithms which are responsive to changing operative and environmental conditions. The control system is particularly adapted for use with multi-module TCUs for cluster tools used in semiconductor fabrication, but is of applicability to other process and equipment meeting similar complex requirements.
It employs a scalable digital control system having a programmable logic controller, together with control and display software for setup, monitoring operator assistance and alarms. Using a touch screen and display unit, the system provides instinctively selectable, organized and unambiguous visual displays that facilitate selection and monitoring of operations. The operator, through observation of historical performance or by using known starting values, can provide initial setpoints for proportional, integral and derivative terms from which the dual adaptive control algorithm undertakes concurrent interrelated control of heating and cooling capabilities. While receiving data as to rate changes and historical changes in the process variables, ambient and cooling medium temperatures the system responds to temperature oscillations by making adjustments in the integral terms in both the dual algorithms. Also, bias values are changed in the heating algorithm in accordance with cooling medium changes.
The dual control algorithms are defined by data stored in the programmable logic controller associated with the data processor, an external section of the controller being changeable so that new programming can be used. Because use of the two oppositely directed thermal exchange capabilities (heating and cooling) is integrated, the heating algorithm is reset and no heating energy is supplied during cooling and non-transitional periods when the actual temperature is less than 0.2xc2x0 C. below the setpoint. However, above that threshold the heating algorithm is reinstated, and a small bias value is added to assist the cooling function on maintaining the target level. Thus at the steady state temperature the heating capability and cooling capability are used concurrently in such fashion as to maintain the thermal transfer fluid at xc2x10.1xc2x0 C. relative to the target level. The system control thus operates with high energy efficiency even though heating and cooling may be used concurrently in steady state. The ramp up or down from one temperature level to another is accomplished rapidly, with minimal undershoot and overshoot. Once temperature setpoint is reached the cooling PID will dominate the control thereby minimizing the heating requirement.
The expandable modules, used along with the central processor unit, comprise digital input expansion modules, thermocouple modules, analog circuit modules (including analog to digital circuits), along with receptacles for additional modules to accommodate further TCU expansion. The digital circuitry includes relay circuits, switching subsystems, and control subsystems. During the constant scanning cycle by the central processor, the processor also concurrently provides operator-requested displays on the touch screen and interface. The displays include a logical progression of different interactive graphics or xe2x80x9cscreensxe2x80x9d to assist in all aspects of the operation. Setpoint screens enable the operator to observe the programmed conditions, and to vary them as appropriate. Information can be viewed that is specific to individual modules, such as flow rate, reservoir and pump pressures, percentage of heating or cooling, and actual temperature. A xe2x80x9csummaryxe2x80x9d screen is available for general monitoring of operations for each module, including sensed conditions such as thermal process fluid actual temperature, and temperature setpoint. A separate screen display provides xe2x80x9cengineering maintenancexe2x80x9d data, including system settings display values, and pump delay characteristics. xe2x80x9cSetupxe2x80x9d screens enable default values for cooling and heating settings to be viewed for the dual PID control loops. On the same screen the operator can observe xe2x80x9cconfigurationxe2x80x9d data, indicating the number and type of TCU modules that are employed, and can also use access to an xe2x80x9cengineering setupxe2x80x9d screen, which provides readings from the sensors in the modules, and includes a running total of system run time and functions for mathematical corrections of desired values. A xe2x80x9cfaultxe2x80x9d screen also provides information as to how to solve a problem that may be encountered, while a separate xe2x80x9chelpxe2x80x9d screen is available to assist with data as to effective corrective efforts.
To provide remote control from the cluster tool system, the setup screen includes a configurable local address, so that a master/slave bus topology type network can be assembled. This network can encompass a variable number of units consisting of up to 4 modules, each of which can be governed by the remote central control in the user""s facility.